1. Field of the Invention
The present invention relates to an ophthalmologic photographing apparatus for photographing a fundus of a subject's eye.
2. Description of the Related Art
Fundus cameras are roughly classified into non-mydriatic fundus cameras and mydriatic fundus cameras. The non-mydriatic fundus camera captures an image of a fundus of a subject's eye with visible light after the subject's eye is observed with near-infrared light. The mydriatic fundus camera captures an image of a fundus of a subject's eye with visible light after the subject's eye, whose pupil is dilated with a mydriatic, is observed with visible light.
In the mydriatic fundus camera, a visible light cut-off filter is inserted in front of a halogen light source in order to prevent a pupil of a subject's eye from being narrowed with observation light. Consequently, only an infrared component of light emitted from the halogen light source is transmitted by the visible light cut-off filter and is irradiated on a fundus of a subject's eye. When photographing a fundus of a subject's eye, the fundus is photographed with visible light by causing a xenon light source to emit light.
Japanese Patent No. 3,004,276 discusses a non-mydriatic fundus camera using a light source for both observation and photographing, which can emit two types of light, i.e., visible light and infrared light, in order to simplify the light source unit employed.
The fundus camera discussed in Japanese Patent No. 3,004,276 switches between photographing light, which is visible light, and illumination light, which is infrared light, by insertion and removal of wavelength selecting filters, such as a visible light cut-off filter and an infrared light cut-off filter, into and out of the optical path of an illumination optical system. Thus, the fundus camera selects a wavelength of light, which is transmitted by the cut-off filter inserted into the optical path. However, the fundus camera using two types of filters, i.e., a visible cut-off filter and an infrared light cut-off filter, has a drawback in that the optical system is complicated and is increased in size.
With recent increases in the intensity of light emitted from light-emitting-diodes (LEDs), fundus cameras using an LED light emitting element as an illumination light source have been proposed. However, the emission wavelength band and the intensity of light emitted from an LED light emitting element are limited. Thus, it is difficult to configure a fundus camera to use a light source for both observation and photographing and to switch between visible light and infrared light using wavelength selecting filters, as discussed in Japanese Patent No. 3,004,276. Thus, a separate illumination light source optical system and observation light source optical system are needed. Consequently, it is difficult to reduce the system in size.